The present invention relates to controllers for controlling the operation of electrical apparatus, such as a pump. The invention finds particular application in the cyclic control of circulating pumps such as a swimming pool filter pump for circulating water from a swimming pool through a filter system. It is to be appreciated, however, that the present invention is also applicable to controlling circulating pumps of other types including water heating and cooling systems, industrial fluid circulating or mixing systems, and the like.
Heretofore, various control systems have been developed for periodically actuating electrical apparatus such as a pump. Some prior art control systems further monitored the electrical apparatus for malfunctions. One such monitored malfunction is an excessive pressure which causes the pump to cut out or shut off.
In many fluid pumping systems, low pressure can be just as deleterious, or more so, than high pressure. For example, a subminimum fluid pressure may be indicative of a loss or leak of the pumped fluid, or the like. Operating the pump at a subminimal pressure may cause the pump motor to overheat or burn out. However, in a periodically operated pump, the fluid pressure commonly drops below a minimal operating pressure between pump actuations. Even upon first actuating the pump, some lead time is commonly required to prime the pump and build the fluid pressure up to normal. Accordingly, if the periodically actuated pump had a low pressure cutoff switch, start up of the pump would be impossible.
The present invention contemplates a new and improved pump control which is responsive to abnormally high as well as abnormally low pumping pressures, yet provides for automatic start up and priming of the pump.